The field of the invention is rotary manual input mechanisms and more particularly, tactile feedback apparatuses used thereon.
There are numerous applications where a knob or crank is manually turned to carry out a control function. In a numerically controlled machine tool, for example, a handwheel may be provided on the control panel to enable the operator to manually "jog" the cutting tool along one or more axes of motion. The amount of handwheel rotation is translated into a digital quantity by a position transducer and is then employed to drive the appropriate servomechanism the desired distance. In such applications, it is essential to provide tactile feedback to the operator so that each time an incremental movement is made, the operator can feel it on the handwheel. The prevailing practice in prior control systems is to employ a detent mechanism to provide the needed tactile feedback. Each detent then corresponds to one incremental movement, for example 0.001 inch of jog, and the operator can feel a click from the detent for each such incremental movement. While detent mechanisms are generally satisfactory, they are mechanically complex and are subject to wear, requiring maintenance for lubrication and adjustment.
To eliminate the need for mechanical detents, other methods of providing tactile feedback have been developed. For example, a stepping motor can be used as the position transducer as described in U.S. Pat. No. 4,553,080 by the assignee of the present invention, wherein the static torque of the stepping motor provides tactile feedback. This approach too is satisfactory, but requires additional components to overcome a basic limitation, which is the possibility of missing pulses when the stepping motor is rotated too slowly. Also, a somewhat complex control circuit is required to convert the signals from the stepping motor into a form suitable for use by an external device.